The present invention relates to a sensor arrangement for detecting the presence of a single axle of a rail vehicle in a short length of a track and to the arrangement of two or more such sensor arrangements along the track.
Such sensor arrangements are used as axle detectors at counting points of axle-counting installations. They must safely detect all axles of a rail vehicle, even if these are spaced short distances apart, as in trucks, and if the vehicle travels at high speed.
So far, axle detectors have mainly employed magnetic sensing devices, which sense a change in a magnetic circuit caused by wheel flanges and tires. These conventional sensing devices are usually attached in pairs to both rails of a track and displaced a few centimeters in relation to one another, so that the passage of an axle causes two axle pulses to be provided which are are shifted in time with respect to each other and whose order is used to additionally determine the direction of movement of the axle (see, for example, an article by G. Frech and K. Schmidt in "Signal und Draht" 59 (1967), No. 11, pp. 165-174).
The conventional axle detectors are permanently connected with the rail. As a result, rail vibrations, which may reach very high acceleration rates, may be transmitted to the respective axle detector. Accordingly, costly and complicated fastening and adjusting elements are required to insure that the mechanical action does not lead to a change in the magnetic circuit. Strong vibrations may also damage the electric components in the axle detector and result in failures. Finally, a magnetic axle detector is sensitive to interference caused by metallic parts hanging down from vehicles, such as electromagnetic rail brakes. To insure that such an axle detector safely responds to each wheel but does not react to electromagnetic rail brakes, precise electrical adjustment is necessary, which ensures error-free operation only if the electromagnetic rail brakes do not hang down from the vehicles too far.